1. Field of the Invention
The present invention relates to an ignition coil for an internal combustion engine. More specifically, the present invention relates to an ignition coil for an internal combustion engine having an open magnetic path structure.
2. Description of Related Art
Conventionally, there are many known forms of ignition coils which supply high voltages to ignition plugs of internal combustion engines.
For example, Japanese Patent Laid Open Publication Nos. Hei-3-154311, Hei-2-228009 and Hei-3-13621 propose a cylindrical ignition coil.
This type of ignition coil should be containable in a plug hole of the internal combustion engine. Therefore, in order to provide powerful ignition sparks to the ignition plug, the ignition coil must be able to generate enough energy while having a small size at the same time.
In this way, the use of bias magnets has been proposed in the prior art but their sole use is not enough to balance both requirements for miniaturization and high-energy output.
An improvement in the iron core shape is one technology that has been proposed for miniaturizing a transformer. For example, Japanese Patent Laid Open Publication Nos. Sho-50-88532, Sho-51-38624, Hei-3-165505, etc. disclose an iron core whose substantially circular cross-section is formed by stacking various silicon sheets.
However, conventional technology was not able to raise the ratio of the area covered by the iron core with the area provided for it (referred to as occupation rate hereinafter) and thus, a high-level of miniaturization was not achieved.
In view of the foregoing problems of the prior art in mind, it is a goal of the present invention to provide a small-sized and high output ignition coil.
Also, the present invention aims to decrease the size and increase the energy output of slender cylindrical ignition coils. Another aim of the present invention is to decrease the size and increase the energy output of the ignition coil by optimizing a magnetic circuit used for the slender cylindrical ignition coil. In addition, the present invention aims to decrease the size and increase the energy output of the ignition coil by optimizing an iron core of the slender cylindrical ignition coil.
To achieve these aims, one aspect of the present invention provides an internal combustion engine ignition coil for supplying high voltages to an ignition plug of an internal combustion engine which includes a case, a cylindrical magnetic path constituting member which is housed in the case, and a coil housed inside the case and disposed at an outer periphery of an iron core of the cylindrical magnetic path constituting member and which includes a primary coil and a secondary coil, wherein the magnetic path constituting member is formed by stacking in a diameter direction of the magnetic path constituting member a plurality of magnetic steel sheets which have different widths with a cross-section in the diameter direction of the magnetic path constituting member being substantially circular, formed by the stacked magnetic steel sheets which define a circle circumscribing the edges of the magnetic steel sheets, the circle having a diameter of no more than approximately 15 mm, formed by the stacked magnetic steel sheets where each individual sheet has a thickness no more than 8% of the diameter of the circle circumscribing the edges of the sheets, formed by the stacked magnetic steel sheets of no less than six kinds of width, formed by the stacked magnetic steel sheets which number at least twelve sheets, and formed so that the stacked magnetic field sheets cover no less than 90% of the area of the circle circumscribing the edges of the sheets.
In this way, when this core is contained in a bobbin having inner contours which correspond to the circumscribing circle, the space that is wasted is reduce to no more than 10%. Thus, the electric voltage conversion efficiency between the coils wound up around the outer periphery of the bobbin can be improved. Also, by shaping the core to be inserted into the bobbin, the metal sheets can thus be held together by just inserting a cylinder stopper whose diameter is slightly smaller than that of the circumscribing circle without no need for fixing by pressing or the like. Thus, movement of the stacked magnetic sheets in the diametrical direction is prevented. Therefore, costs are lowered because there is no need for expensive press molds and the like.
Another aspect of the present invention provides an ignition coil wherein the plurality of stacked metal sheets have at least eleven kinds of width, the plurality of stacked metal sheets includes at least twenty-two sheets; and the plurality of stacked magnetic field sheets cover no less than 95% of the area of the circle circumscribing the edges of the sheets. In this way, the wasted space for the iron core is reduced to no more than 5%.
In another aspect of the present invention, a magnetic sheet having a thickness of no greater than 0.5 mm is stacked with other magnetic sheets having the same thickness. In this way, energy loss due to eddy currents can be reduced and thus, drops in the electrical voltage conversion efficiency are prevented.
In yet another aspect of the present invention, the magnetic sheets are directional silicon steel sheets.
A yet further aspect of the present invention provides an ignition coil wherein a cross-sectional area SC of the magnetic path constituting member in the diameter direction is 39xe2x89xa6SCxe2x89xa654 and wherein the coil housing part of the case has an external diameter of less than 24 mm.
In this way, because the diameter direction cross-sectional area SC of the magnetic path constituting member is set to SCxe2x89xa739 (mm2), it is possible to produce the 30 mJ of electrical energy that the internal combustion engine demands, and because the diameter direction cross-sectional area SC is set to SCxe2x89xa654 mm2, it is possible to make the external diameter of the case to be less than 24 mm. Thus, without making the case external diameter larger than 24 mm, it is possible to produce the 30 mJ of electrical energy that the internal combustion engine demands. Therefore, the ignition coil for an internal combustion engine can be fitted in a plug tube having an internal diameter of 24 mm and the electrical energy necessary to effect spark discharge can be supplied to a spark plug.
An additional aspect of the present invention provides an ignition coil wherein the magnetic path constituting member defines a circle circumscribing the magnetic path constituting member where the circle has a diameter of no more than 8.5 mm.
Another aspect of the present invention provides an ignition coil wherein the magnetic path constituting member is formed by stacking bar-shaped magnetic steel sheets; and wherein the magnetic path has magnets disposed at both of its ends.
In this way, because the magnetic path constituting member is made by laminating steel sheets, eddy current losses can be reduced. As a result, there is the effect of increasing the electrical energy produced in the coil.
A yet further aspect of the present invention provides an ignition coil wherein surface ends of the magnetic path constituting member which is in contact with magnets is provided with a ditch in a direction that intersects with the plurality of stacked metal sheets with the plurality of stacked metal sheets being joined together by the ditch.
A further aspect of the present invention is that a ratio of an area Sm, of the end surfaces of the magnets facing the magnetic path constituting member with the cross-sectional area Sc of the magnetic path constituting member is so set that 0.7xe2x89xa6SM/Scxe2x89xa61.4.
In this way, since a magnetic bias is applied because magnets are disposed on both ends of the magnetic path constituting member and the ratio of the area SM of the end surfaces of the magnets facing the magnetic path constituting member and the diameter direction cross-sectional area SC of the magnetic path constituting member is set to SM/SCxe2x89xa70.7, a magnet bias flux acts well, and also because SM/SCxe2x89xa61.4 is set, it is possible to make the external diameter of the case to be less than 24 mm. As a result, there is the effect of further increasing the electrical energy produced in the coil without making the case external diameter larger than 24 mm. Also, because the necessary number of magnets is two, it will be possible to reduce the number of magnets used more than with a conventional ignition coil for an internal combustion engine and also it will be possible to provide a cheap ignition coil for an internal combustion engine.
An additional aspect of the present invention is that the coil is wound up along an axial direction of the magnetic path constituting member with a ratio of an axial length Lc of the magnetic path constituting member with a winding width L of the coil being set so that 0.9xe2x89xa6Lc/Lxe2x89xa61.2 and winding width L (mm) being 50xe2x89xa6Lxe2x89xa690.
In this way, because the ratio of the axial length Lc of the magnetic path constituting member and the winding width L over which the coil is wound is set to Lc/Lxe2x89xa70.9, the magnets disposed on the two ends of the magnetic path constituting member do not greatly enter the range of the coil winding width L and reduction of the effective flux of the coil due to the diamagnetic field of the magnets is suppressed, and because Lc/L is set to Lc/Lxe2x89xa61.2 the spacing of the magnets does not become too wide with respect to the coil winding width L and the magnets can be positioned on the two ends of the magnetic path constituting member in the range wherein a magnet bias flux acts well. Also, it is possible to further increase the electrical energy produced in the coil without increasing the case external diameter. As a result, since in correspondence with the secondary energy amount which the internal combustion engine demands, the external diameter of the case can be set smaller than for example 24 mm, and the necessary number of magnets can be one or a construction that does not use any magnets can also be adopted and in doing so, a cheap ignition coil can be provided for an internal combustion engine.
One other aspect of the present invention provides an internal combustion engine ignition coil for supplying a high voltage to an ignition plug of an internal combustion engine, where the ignition coil includes a case, a cylindrical magnetic path constituting member which is housed in the case, and a coil housed inside the case and disposed at an outer periphery of an iron core of the magnetic path constituting member and which includes a primary coil and a secondary coil, wherein an area Sc (mm2) of a cross-section of the magnetic path constituting member perpendicular to the length of the member is 39xe2x89xa6Scxe2x89xa654; and wherein an outer diameter of the coil housing part of the case is less than 24 mm.
Another aspect of the present invention is that the cross-section of the magnetic path constituting member is substantially circular in shape where its cross-section defines a circle which circumscribes the cross-section and has a diameter of no more than 8.5 mm.
An additional aspect of the present invention provides an ignition coil wherein the magnetic path constituting member being formed by stacking magnetic steel sheets of different width.
Another aspect of the present invention is that magnets are disposed at both ends of the magnetic path constituting member.
In a further aspect of the present invention, a ratio of an area Sm of the end surfaces of the magnets facing the magnetic path constituting member with the cross-sectional area Sc of the magnetic path constituting member is set so that 0.7xe2x89xa6SM/Scxe2x89xa61.4.
A yet further aspect of the present invention is that the coil is wound up along an axial direction of the magnetic path constituting member, a ratio of an axial length Lc of the magnetic path constituting member with a winding width L of the coil is set that 0.9xe2x89xa6Lc/Lxe2x89xa61.2, and the winding width L (mm) is 50xe2x89xa6Lxe2x89xa690.